Log4net
The Basics
Three parts : configuration , setup , call
Configuration - done via app.config (desktop application) or web.config (web application)
Setup - set up and instantiate connection with Log4Net
Call - write to log
Logging Levels
There are 7 logs level arranged from the highest priority at the top
- OFF - nothing gets logged (cannot be called)
- FATAL
- ERROR
- WARN
- INFO
- DEBUG
- ALL - everything gets logged (cannot be called)
The Configuration
Root
You must have one root section.
It house the minimal level for all logger.
All logger inherit it
<root> <level value="INFO"/> <appender-ref ref="FileAppender"/> <appender-ref ref="TraceAppender" /> </root>
Additional Loggers
Sometimes you will want to know more about a particular part of your application. log4net anticipated this by allowing you to specify additional logger references beyond just the root logger. For example, here is an additional logger that I have placed in our config file to log to the output messages that occur inside the
OtherClass class object:<logger name="Log4NetTest.OtherClass">
<level value="DEBUG"/>
<appender-ref ref="TraceAppender"/>
</logger>
Note that the logger name is the full name of the class including the namespace. If you wanted to monitor an entire namespace, it would be as simple as listing just the namespace you wanted to monitor. I would recommend against trying to re-use appenders in multiple loggers. It can be done, but you can get some unpredictable results.
In a config file where there will (potentially) be more information stored beyond just the log4net configuration information, you will need to specify a section to identify where the log4net configuration is housed. Here is a sample section that specifies that the configuration information will be stored under the XML tag "
log4net":<configSections>
<section name="log4net"
type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
</configSections>
Appender (General)
An appender is the name for what logs the information. It specifies where the information will be logged, how it will be logged, and under what circumstances the information will be logged. While each appender has different parameters based upon where the data will be going, there are some common elements. The first is the name and type of the appender. Each appender must be named (anything you want) and have a type assigned to it (specific to the type of appender desired). Here is an example of an appender entry:
<appender name="TraceAppender" type="log4net.Appender.Trace
Appender">
Layout
Inside of each appender must be a layout section. This may be a bit different depending on the type of appender being used, but the basics are the same. You need a type that specifies how the data will be written. There are multiple options, but the one that I suggest you use is the pattern layout type. This will allow you to specify how you want your data written to the data repository. If you specify the pattern layout type, you will need a sub-tag that specifies a conversion pattern. This is the pattern by which your data should be written to the data repository. I will give a more detailed description of your options for the conversion patterns, but for now, here is an example of the layout tag with the pattern layout specified:
Collapse | Copy Code<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger [%ndc]
- %message%newline"/>
</layout>
Conversion Patterns
Filters
See http://www.codeproject.com/Articles/140911/log4net-Tutorial
Appenders
Each type of appender has its own set of syntax based upon where the data is going. The most unusual ones are the ones that log to databases. I will list a few of the ones that I think are most common. However, given the above information, you should be able to use the examples given online without any problems. The log4net site has some great examples of the different appenders. As I have said before, I used the log4net documentation extensively and this area was no exception. I usually copy their example and then modify it for my own purposes.
Trace Appender
It writes to the output window. This particular filter outputs a value like "2010-12-26 15:41:03,581 [10] WARN Log4NetTest.frmMain - This is a WARN test." It will include a new line at the end.
<appender name="TraceAppender" type="log4net.Appender.TraceAppender"> <layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date{ABSOLUTE}
[%thread] %level %logger - %message%newline"/>
</layout>
<filter type="log4net.Filter.StringMatchFilter">
<stringToMatch value="test" />
</filter>
<filter type="log4net.Filter.DenyAllFilter" />
</appender>
File Appender
This appender will write to a text file. The big differences to note here are that we have to specify the name of the text file (in this case, it is a file named mylogfile.txt that will be stored in the same location as the executable), we have specified that we should append to the file (instead of overwriting it), and we have specified that the
FileAppender should use the Minimal Lock which will make the file usable by multiple appenders.<appender name="FileAppender" type="log4net.Appender.FileAppender">
<file value="mylogfile.txt" />
<appendToFile value="true" />
<lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %level %logger - %message%newline" />
</layout>
<filter type="log4net.Filter.LevelRangeFilter">
<levelMin value="INFO" />
<levelMax value="FATAL" />
</filter>
</appender>
Rolling File Appender
This is an appender that should be used in place of the file appender whenever possible. The purpose of the rolling file appender is to perform the same functions as the file appender but with the additional option to only store a certain amount of data before starting a new log file. This way, you won't need to worry about the logs on a system filling up over time. Even a small application could overwhelm a file system given enough time writing to a text file if the rolling option were not used. In this example, I am logging in a similar fashion to the file appender above, but I am specifying that the log file should be capped at 10MB and that I should keep up to 5 archive files before I start deleting them (oldest gets deleted first). The archives will be named with the same name as the file, only with a dot and the number after it (example:mylogfile.txt.2 would be the second log file archive). The
staticLogFileName entry ensures that the current log file will always be named what I specified in the file tag (in my case, mylogfile.txt).<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
<file value="mylogfile.txt" />
<appendToFile value="true" />
<rollingStyle value="Size" />
<maxSizeRollBackups value="5" />
<maximumFileSize value="10MB" />
<staticLogFileName value="true" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %level %logger - %message%newline" />
</layout>
</appender>
ADO.NET Appender
See http://www.codeproject.com/Articles/140911/log4net-TutorialThe Code
Once you have a reference to the log4net DLL in your application, there are three lines of code that you need to know about. The first is a one-time entry that needs to be placed outside of your class. I usually put it right below my
using statements in the Program.cs file. You can copy and paste this code since it will probably never need to change (unless you do something unusual with your config file). Here is the code:[assembly: log4net.Config.XmlConfigurator(Watch = true)]
The next entry is done once per class. It creates a variable (in this case called "
log") that will be used to call the log4net methods. This code is also code that you can copy and paste (unless you are using the Compact Framework). It does a System.Reflection call to get the current class information. This is useful because it allows us to use this code all over but have the specific information passed into it in each class. Here is the code:private static readonly log4net.ILog log = log4net.LogManager.GetLogger
(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
The final code piece is the actual call to log some piece of information. This can be done using the following code:
log.Info("Info logging");
Notice that you can add an optional parameter at the end to include the exception that should be logged. Include the entire exception object if you want to use this option. The call is very similar, and it looks like this:
log.Error("This is my error", ex);
ex is the exception object. Remember that you need to use the %exception pattern variable in your appender to actually capture this exception information.Config File Template
While you can look at the example code I have posted to see a config file in action, based upon some of the difficulties people were experiencing, I decided to post a config file template to help readers visualize where each of the config file pieces will go. I have given you a blank template below. I have also labeled each section with which level it is in so that, in case the formatting doesn't make it obvious, you know how each item relates to all the others up and down the tree.
Collapse | Copy Code<!--This is the root of your config file-->
<configuration> <!-- Level 0 -->
<!--This specifies what the section name is-->
<configSections> <!-- Level 1 -->
<section name="log4net"
type="log4net.Config.Log4NetConfigurationSectionHandler,
log4net"/> <!-- Level 2 -->
</configSections>
<log4net> <!-- Level 1 -->
<appender> <!-- Level 2 -->
<layout> <!-- Level 3 -->
<conversionPattern /> <!-- Level 4 -->
</layout>
<filter> <!-- Level 3 -->
</filter>
</appender>
<root> <!-- Level 2 -->
<level /> <!-- Level 3 -->
<appender-ref /> <!-- Level 3 -->
</root>
<logger> <!-- Level 2 -->
<level /> <!-- Level 3 -->
<appender-ref /> <!-- Level 3 -->
</logger>
</log4net>
</configuration>
FAQs
- Why can't I write to my text file? log4net runs under the privileges of the active user. Make sure that the active user has rights to create/modify/delete the specified text file.
- Why aren't certain events being logged? Most likely, this is because you have a filter in place. Remember that the root entry can have an overall minimum log filter that specifies no event gets logged below this level. The actual appender can also have a level filter, or you could have the deny all in place too early.
- Why am I logging events that I don't want? Most likely you have set a filter improperly. Either you forgot the deny all filter, or you included a level range filter first.
- Why am I getting a compile error? If you get an error similar to "The referenced assembly "log4net" could not be resolved because it has a dependency on "System.Web, Version=4.0.0.0 ...", then you haven't changed your target framework to ".NET Framework 4". Change that and this error, along with others that cascade from it, will go away. Note: this has been fixed in the new version of log4net. You should no longer need to do this.
- How do I use this in ASP.NET? Using this information in ASP.NET is the same as using it in a desktop application. The major difference is that the config file is the web.config file instead of the app.config file.
- Why can't I get my ADO.NET appender to log anything? If you look over all of the settings and they look right, chances are that you are experiencing the pain of the
bufferSizeconfiguration. Change thebufferSizeto 1 and it will attempt to log every message you send right away. If this still does not work, the issue is your configuration.
Source sample
Following is a simple ASP.Net sample
WebSiteTestLog4Net
Default.aspx.cs
[assembly: log4net.Config.XmlConfigurator(Watch = true)]
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
log.Debug("Debug logging _Default");
log.Info("Info logging _Default");
log.Warn("Warn logging _Default");
log.Error("Error logging _Default");
log.Fatal("Fatal logging _Default");
Class1.callMe();
}
private static readonly log4net.ILog log = log4net.LogManager.GetLogger
(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
}
Class1.cs
////// Summary description for Class1 /// public class Class1 { public static void callMe() { log.Debug("Debug logging Class1"); log.Info("Info logging Class1"); log.Warn("Warn logging Class1"); log.Error("Error logging Class1"); log.Fatal("Fatal logging Class1"); } private static readonly log4net.ILog log = log4net.LogManager.GetLogger (System.Reflection.MethodBase.GetCurrentMethod().DeclaringType); }
Web.config
Running the application will produce the following :
A file name mylogfile1 under the web site root :
Visual studio Output windows
Sources :
Nathan
